Update Table: ProjectAffiliateXref

### Overview

We need to update the ProjectAffiliateXref table model to have the correct names for fields.

#### Details

- The initial model issue: #65
- Discussion leading to this change is here: [Replace with ISSUE URL OR OTHER LINK OPTIONAL]

### Action Items

- Update existing Django model

- [x] In the files indicated by Resource 1.01, Change the following items in the code

| Current Name in code | Updated Name | Updated Type (may already be this type) | FK Table | FK Table Issue(s) |
| -------------------- | ------------ | --------------------------------------- | -------- | ----------------- |
| affiliate_id | affiliate | int | affiliate | #76 & #30 & #52 |
| project_id | project | int | project | #16 |
| ended_at | ended | date (not datetime) | |

- [x] Write a test for the new relationships this model will have with other models (e.g., creating a user and assigning them a set of permissions on a project) if any.
- [x] Update API end point
- [x] Update API unit tests
- [x] generate a schema table description (see resources 1.04), post it in a comment below, and add a link to it in the Update Schema dependency issue
- [x] Document the endpoint in ReDocs (see resources 1.05)

### FK status
- #76
- #30
- #52
- #16

### Resources
- 1.01 Code locations
- 1.01.01 [/app/core/models.py](https://github.com/hackforla/peopledepot/blob/main/app/core/models.py)
- 1.01.02 [/app/core/admin.py](https://github.com/hackforla/peopledepot/blob/main/app/core/admin.py)
- 1.01.03 [/app/core/api/serializers.py](https://github.com/hackforla/peopledepot/blob/main/app/core/api/serializers.py)
- 1.01.04 [/app/core/api/views.py](https://github.com/hackforla/peopledepot/blob/main/app/core/api/views.py)
- 1.02 [People Depot Resources wiki page](https://github.com/hackforla/peopledepot/wiki/Resources-and-Links) for links
- ERD
- Table and Field Definitions
- API Endpoint
- 1.03 Spreadsheet: [PD: Table and field explanations, Current Field Permission tab](https://docs.google.com/spreadsheets/d/1x_zZ8JLS2hO-zG0jUocOJmX16jh-DF5dccrd_OEGNZ0/edit?gid=749942651)
-1.03.01 [ProjectAffiliateXref filter](https://docs.google.com/spreadsheets/d/1x_zZ8JLS2hO-zG0jUocOJmX16jh-DF5dccrd_OEGNZ0/edit?gid=749942651#gid=749942651&fvid=1025339388)
- 1.04 [Instructions for how to generate a schema table description](https://hackforla.github.io/peopledepot/contributing/howto/generate-db-table-description/)
- 1.05 [Instructions for how to Document End point](https://hackforla.github.io/peopledepot/contributing/howto/add-model-and-api-endpoints/#add-viewset) step 3